Review: restrict Reject option to reviewers

Users have been discouraged from using the Reject action on their own
extensions for quite awhile. This disrupts the diff review flow since
new submissions need to be manually checked to ensure we don't miss
buggy/malicious in a version rejected by a user.

fixes #99
1 job for master in 5 minutes and 24 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #817289
privileged
test

00:05:24